Mobile communication network services can be divided into two categories in view of a technical implementation: one is Circuit Switched (CS) services, such as voice services and SMS services; the other is Packet Switched (PS) services, such as web browsing services.
In order to effectively use mobile network resources, the 3GPP proposes Long Term Evolution (LTE), which is a system architecture completely based on packets, and supports real-time services and voice session services through the packet architecture. The LTE based system is referred to as an EPS, and the EPS architecture of the 3GPP is shown in FIG. 1.
Roaming is a major function of the mobile communication network, different operators can allow subscribers to share their networks by a roaming agreement, and roaming commonly occurs between networks of operators which are deployed in different geographical regions. In order to identify an original network to which the subscriber belongs and a new network to which the subscriber roams, both of the networks are generally distinguished by a home location and a visited location. When the network properties of the home location and the visited location are the same, for example, both are the LTE or Universal Mobile Telecommunications System (UMTS) networks, the roaming is referred to as an in-band roaming. Even being the in-band roaming, services provided by the home network and the visited network may also be different.
The SMS is for the purpose of transmitting information through a Service Centre (SC) between a Short Message Entity (SME) and a user equipment. The SMS includes Mobile Originated (MO) services and Mobile Terminating (MT) services, i.e., including the user equipment transmitting or receiving information. The network architecture of the transmission of the CS SMS is shown in FIG. 2, an SME and an SMS-SC are included outside the 3GPP or GSM network, and an SMS Gateway Mobile Switching Center (GMSC) or an SMS Interconnect Mobile Switching Center (IWMSC), an SMS router, a MSC or Visitor Location Register (VLR) or a Service GPRS Support Node (SGSN) and a Mobile Station (MS) are included in the 3GPP or GSM network.
With respect to the demand for LTE packet access, the 3GPP proposes requirements of PS-only SMS, i.e., the SMS being implemented through the PS domain, the PS-only here includes two cases: one is that the SMS can only be implemented through the PS domain; and the other is that if the SMS cannot be implemented through the PS, it can also be implemented through the CS, i.e., PS-preferred.
At present, the SMS in the 3GPP can be implemented through a CS domain or a PS domain, wherein the traditional 2/3G networks generally use the CS domain SMS, for the EPS system, the core network uses packet architecture, there are the following several schemes for implementing the EPS SMS: SMS over IP Multimedia Subsystem (IMS), CS FallBack (CSFB), SMS over SGs etc., and the EPS structural diagram of CSFB and SMS over SGs are illustrated in FIG. 3. All the above schemes are based on the auxiliary systems or add the interfaces from the PS to the circuit domain to implement the SMS, and in the related art, there has no specific solutions for the PS SMS in the EPS. For the scene of LTE in-band roaming, how to implement the SMS also has not been solved.